The present invention relates to a method for treating the surface of a ceramic hybrid substrate including ceramic surface areas and metallic surface areas.
The use of ceramic (glass ceramic) hybrid substrates is conventional, for example, in the construction of electrical circuit arrangements. Such electrical circuit arrangements are used in various industrial areas, for example, in the area of motor vehicle electronics for engine control, anti-lock braking control, etc. The ceramic hybrid substrates contain processed electronic components and metallic conducting tracks, via which contacting of the hybrid substrates can occur. It is conventional that such ceramic hybrid substrates are obtainable by laminating individual function layers that may have electrical connecting leads, integrated circuit constituents, micromechanical structures, etc. Such a sandwich arrangement that includes several function layers is subsequently sintered so that the finished ceramic hybrid substrate is formed. The finished ceramic hybrid substrate therefore has a surface structure that includes some ceramic surface areas and some metallic surface areas (conducting tracks, pads) embedded in them. By miniaturizing such ceramic hybrid substrates, the distance between adjacent metallic areas can be in the range of  less than 100 xcexcm. In order to be able subsequently to contact such metallic surface areas integrated in the so-called fine line technology, for example, by bonding, the application of electrically conductive adhesives, etc., it is conventional that the metallic surface areas can be finished, for example, by applying a contact metal (silver, gold, or the like) to the metallic surface areas using a chemical deposition process. In this case, the ceramic hybrid substrates are treated in chemical baths, some of which contain aggressive and etching substances that attack the surface of the ceramic surface areas. Moreover, it is disadvantageous that, during the deposition of the contact metal in chemical baths, deposits of metals can also occur on the ceramic surface areas which canxe2x80x94in particular in view of the small distances between the metallic surface areasxe2x80x94result in short circuits. Moreover, it is disadvantageous that during a subsequent contacting of the metallic surface areas, for example, by an electrically conductive adhesive, the adhesive tends to flow (bleed), so that short circuits can occur between adjacent metallic areas.
In contrast, the method according to the present invention and the ceramic hybrid substrate according to the present invention provides the advantage that a subsequent machining of the metallic surface areas or a subsequent contacting of the metallic surface areas may occur, with a reduced tendency of short circuits between adjacent metallic surface areas. By esterifying the ceramic surface areas of the ceramic hybrid substrate, the ceramic surface areas may be protected selectively during the subsequent postxe2x80x94treatments in chemical baths. As a result of the esterification, a monomolecular surface layer is formed on the ceramic surface areas which is resistant to chemicals and heat, so that metal coatings chemically deposited in particular on the metallic surface areas are not able to deposit on the ceramic surface areas. Moreover, this selective esterifying of the ceramic surface areas causes a change in their surface tension, so that electrically conductive adhesives applied to the metallic surface areas do not tend to flow onto the ceramic surface areas.
The surface of the ceramic hybrid substrate may be treated with a solution including organic constituents tailored to the ceramic surface. This treatment may occur via a dipping bath, flow wave soldering, spraying on, spreading on with a doctor, etc. By wetting the surface with the solution including the organic constituents, the solution is deposited in micropores of the ceramic surface areas. Via a subsequent heat treatment, crosslinking of the organic constituents of the solution with lattice structures on the ceramic surface areas may occur. This results in the formation of the chemically and thermally stable (resistant) surface coating of the ceramic surface areas. By a subsequent removal of non-crosslinked residues of the solution including the organic constituents, the solution may be removed from the metallic surface areas, where no adhering effect (crosslinking) occurs. The metallic surface areas in the processed form and with the original properties are thus available for further processing.
An example method according to the present invention may be used for ceramic hybrid substrates whose manufacture is silicon-based, in which the ceramic surface areas are treated with silicon as a solution containing an organic component (siloxane). The concentrations of organic silicon compounds may be between 0.1 and 1% of the solutionxe2x80x94relative to the total volume. Using such a treatment, a silicon oxide or silicon dioxide surface layer that has good resistance to chemical and thermal influences may be achieved after the crosslinking of the solution with the ceramic surface areas.